1. Field of the Invention
The present invention relates to a dielectric filter unit, a duplexer, and a communication apparatus, used in microwave frequency bands, for example.
2. Description of the Related Art
As a dielectric duplexer to be used in portable telephones, and so on, duplexers in which resonator holes constituting a plurality of dielectric resonators are arranged in a dielectric block have been known. FIG. 9 shows an example of a prior art dielectric duplexer. In the dielectric duplexer 1, resonator holes 3a, 3b, and 3c constituting a transmission filter 7 and resonator holes 3d, 3e, and 3f constituting a reception filter 8 are given in a dielectric block 2 in the form of a rectangular solid.
The resonator holes 3a through 3f are identical in shape to each other and are of a stepped hole having a large-sectional area portion 4a and a small-sectional area portion 4b linked to the large-sectional area portion 4a. On the inner surface of the resonator holes 3a through 3f an inner conductor 5 is formed, respectively. In each of the inner conductors 5, a nonconductive portion indicated by g is disposed in the vicinity of the end portion on the side of the large-sectional area portion 4a is provided, and this portion is made open-ended. On the outer surface of the dielectric block 2 an antenna terminal ANT, a transmission terminal Tx, and a reception terminal Rx are provided, and at the same time an outer conductor 6 is formed on nearly all the surface except these terminals ANT, Tx, and Rx. Each of the inner conductors 5 is connected to the outer conductor 6 at the end portion on the side of the small-sectional area portion 4b, and this portion is made short-circuited.
Then, in the prior art dielectric duplexer 1, because all the resonator holes 3a through 3f were the same in shape, the area ratio of the large-sectional area portion 4a to the diameter of the small-sectional area portion 4b of the resonator holes 3a through 3c constituting the transmission filter 7 (hereinafter, referred to as step ratio) was the same as the step ratio of the resonator holes 3d through 3f constituting the reception filter 8. Consequently, the adjustment of the center frequency of the transmission filter 7 or reception filter 8 has been carried out by moving the location of the nonconductive portion g of the inner conductor 5 or by altering the length in the axial direction of the resonator holes 3a through 3f of the dielectric block 2.
For example, when the center frequency of the transmission filter 7 is 1950 MHz and the center frequency of the reception filter 8 is 2140 MHz, if the dielectric constant xcex5r of the dielectric block 2 is 21.4, the length in the axial direction of the resonator holes 3a through 3c of the transmission filter 7 becomes longer than the length in the axial direction of the resonator holes 3d through 3f of the reception filter 8 to result in the difference of 0.7 mm. Because of this, when the transmission filter 7 and reception filter 8 had been made separately and then both of them were joined and connected to produce the dielectric duplexer 1, because the length of the dielectric block of the transmission filter 7 and length of the dielectric block of the reception filter 8 in the axial direction of the resonator holes are different, a play and a positional discrepancy were likely to occur when they are joined and connected.
To overcome the above problems, preferred embodiments of the present invention provide a dielectric filter unit, a duplexer, and a communication apparatus in which the adjustment of the center frequency of each of the filters can be made without moving the location of the nonconductive portion of the inner conductor or without altering the length of the dielectric block in the axial direction of the resonator holes.
One preferred embodiment of the present invention provides a dielectric filter unit comprising: a dielectric block having a pair of opposing end surfaces; a plurality of resonator holes respectively passing through the pair of opposing end surfaces of the dielectric block and having a large-sectional area portion and a small-sectional area portion connected to the large-sectional area portion; an inner conductor disposed on the inner surface of each of the resonator holes; an outer conductor disposed on the outer surface of the dielectric block; at least one of the resonator holes constituting a first filter; at least one of the remaining resonator holes constituting a second filter; and the area ratio of the large-sectional area portion to the diameter of the small-sectional area portion of the resonator hole of the first filter being different from the area ratio of the large-sectional area portion to the diameter of the small-sectional area portion of the resonator hole of the second filter.
In the above described dielectric filter unit, at least one of the large-sectional area portions or at least one of the small-sectional area portions of the resonator holes may be a circular shape, a triangle shape, a square shape, a polygon shape, and so on.
In the above described dielectric filter unit, the inner conductor may have a nonconductive portion in the vicinity of one open end portion of the resonator hole.
In the above described dielectric filter unit, the outer conductor may be extended to the pair of end surfaces of the dielectric block where the resonator holes passing through; the outer conductor disposed on one of the pair of end surfaces is electrically separated into an internal portion and a surrounding portion by a strip-like nonconductive portion surrounding each resonator hole; the internal portion includes each resonator hole; and the surrounding portion surrounds the internal portion.
In the above described dielectric filter unit, the dielectric block may be divided into each of the resonator holes.
In the above described dielectric filter unit, the first filter may comprise a dielectric block which is divided into each of the resonator holes; and the second filer comprises a single dielectric block.
Another preferred embodiment of the present invention provides a duplexer comprising the dielectric filter unit.
Yet another preferred embodiment of the present invention provides a communication apparatus comprising either one of the above described dielectric filter or the above described duplexer.
According to the above described structure and arrangement, the center frequency of each filter is adjusted by altering the ratio (step ratio) of the diameter of the large-sectional area portion to the diameter of the small-sectional area portion of each of the resonator holes. That is, when the step ratio is increased, the step portion formed between the large-sectional area portion and small-sectional area portion is heightened. Accordingly, as the conductor path of the inner conductor runs along the surface of the step portion, the path is lengthened that much and the center frequency of the filter is increased. On the contrary, when the step ratio is reduced, the center frequency of the filter decreases. Therefore, without moving the location of the nonconductive portion of the inner conductor or without altering the length of the dielectric block of each filter in the axial direction of the resonator holes the center frequency of the filter is adjusted.
And as a duplexer and communication apparatus according to the present invention are made up of dielectric filter units having the above characteristics and accordingly the length of the dielectric block of each filter in the axial direction of the dielectric holes can be made uniform, the processing for assembly of the duplexer and communication apparatus becomes easy.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.